Guides · Soil
What to plant in clay soil
How to know you have it: It rolls into a sausage in your hand when damp, cracks in August, and holds a puddle for a day after rain.
Clay is not a poor soil. It is a rich soil with a drainage problem, and almost every plant that fails in it fails for one of two reasons: it was planted in a hole that filled with water like a bucket, or it was planted while the ground was wet and the soil was smeared into a seal.
So the work is not to replace the clay. It is to stop water sitting where roots are. Plant on a slight mound, break the sides of the hole rather than glazing them with a spade, and backfill with the soil you dug out — not with bought compost, which turns the hole into a sump the roots will refuse to leave.
Then choose plants that never resent a wet winter. Mediterranean silver-leaved plants are the ones that die: lavender, santolina, rosemary and cistus rot at the collar in cold wet ground unless you raise them clear of it. Field maple, hornbeam, viburnum, hydrangea, Molinia and hardy geranium do the opposite — they take heavy ground and thrive in it.
The four rules
- 01Plant in autumn or early spring, never when the soil sticks to your boots.
- 02Mound anything drought-loving 20 to 30 cm above the surrounding level, in a gravel-rich mix.
- 03Mulch 5 cm every year. Clay improves from the top down, not from digging.
- 04Never dig or walk on wet clay: one wet afternoon undoes a season of structure.
What we plant in clay soil
These are the species our own plant database will draw from for a site on clay soil — 4 trees, 2 hedging species, 3 shrubs, 3 grasses, 4 perennials, 3 edibles. Prices are French retail nursery prices per plant, 2026, at the pot size given.
| Species | Type | Height | Spacing | Price | Why it belongs |
|---|---|---|---|---|---|
| Field mapleAcer campestre · Érable champêtre | tree | 8,00 m | 6,00 m | 165 € | The reliable small native canopy for heavy ground; takes clay and wind without sulking. |
| OliveOlea europaea · Olivier | tree | 5,00 m | 5,00 m | 240 € | Needs sharp drainage; on clay it is planted on a raised gravel mound, never in a sump. |
| Snowy mespilusAmelanchier lamarckii · Amélanchier | tree | 5,00 m | 4,00 m | 145 € | Three seasons out of one small tree: white blossom, edible fruit, red autumn. |
| Sweet cherryPrunus avium · Cerisier | tree | 7,00 m | 6,00 m | 78 € | Prune only in summer: a winter cut on a cherry invites bacterial canker. |
| HornbeamCarpinus betulus · Charme | hedge | 2,00 m | 0,33 m | 6 € | Holds its brown leaf through winter and is the cheapest good hedge on clay. |
| SilverberryElaeagnus × ebbingei · Chalef | hedge | 2,50 m | 0,60 m | 15 € | Evergreen, salt- and wind-proof: the hedge for an exposed or coastal boundary. |
| Japanese hollyIlex crenata 'Dark Green' · Houx crénelé | shrub | 0,60 m | 0,50 m | 14 € | Used instead of box: same clipped form, and box moth does not touch it. |
| LaurustinusViburnum tinus · Laurier-tin | shrub | 2,50 m | 1,20 m | 16 € | Evergreen screen that flowers in January, which is when you need it. |
| Panicled hydrangeaHydrangea paniculata 'Limelight' · Hortensia paniculé | shrub | 2,00 m | 1,20 m | 18 € | The one hydrangea that takes real sun in the north and heavy soil everywhere. |
| Autumn moor grassSesleria autumnalis · Seslérie d'automne | grass | 0,50 m | 0,40 m | 7 € | Plant in blocks as a low matrix: it closes the ground and stops weeding. |
| Japanese forest grassHakonechloa macra · Herbe du Japon | grass | 0,40 m | 0,40 m | 12 € | The best grass for shade, and it never seeds itself where you did not want it. |
| Purple moor grassMolinia caerulea 'Transparent' · Molinie | grass | 1,40 m | 0,70 m | 11 € | One of the few good grasses for heavy, damp ground. |
| Hardy geraniumGeranium × oxonianum 'Claridge Druce' · Géranium vivace | perennial | 0,50 m | 0,50 m | 6 € | Covers ground under shrubs on heavy soil and asks for one cut a year. |
| Lenten roseHelleborus × hybridus · Hellébore | perennial | 0,50 m | 0,50 m | 14 € | Flowers in February under the canopy, when nothing else does. |
| Soft shield fernPolystichum setiferum · Polystic à soies | perennial | 0,70 m | 0,60 m | 11 € | Evergreen fern, unfazed by dry shade once its second year is past. |
| Wood sageSalvia nemorosa 'Caradonna' · Sauge des bois | perennial | 0,60 m | 0,40 m | 7 € | Flowers twice if you cut it back hard after the first flush. |
| Autumn raspberryRubus idaeus 'Zeva' · Framboisier remontant | edible | 1,60 m | 0,50 m | 7 € | An autumn variety is cut to the ground each February: no canes to tie in. |
| BlackcurrantRibes nigrum 'Andega' · Cassis | edible | 1,50 m | 1,50 m | 12 € | Fruits on last year's wood: take a third of the oldest stems out every winter. |
| Garden mintMentha spicata · Menthe verte | edible | 0,60 m | 0,40 m | 5 € | Only ever planted in a sunken pot. In open ground it takes the bed. |
What we would not plant here
Each of these is a good plant on the ground it was bred for, and a mistake on yours. This is the list our own palette leaves out for a site on clay soil.
- 01Lavender (Lavandula × intermedia 'Grosso') — wants sand, chalk or loam: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 02Rosemary (Salvia rosmarinus) — wants sand, chalk or loam: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 03Cotton lavender (Santolina chamaecyparissus) — wants sand, chalk or loam: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 04Rock rose (Cistus × purpureus) — wants sand, chalk or loam: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 05Golden oats (Stipa gigantea) — wants sand, loam or chalk: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 06Yarrow (Achillea 'Terracotta') — wants sand, loam or chalk: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 07Thyme (Thymus vulgaris) — wants sand or chalk: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 08Mediterranean spurge (Euphorbia characias subsp. wulfenii) — wants sand, chalk or loam: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
- 09Strawberry (Fragaria × ananassa 'Mara des Bois') — wants loam or sand: in cold wet ground it rots at the collar over winter, and only survives here raised 20 to 30 cm on a gravel mound.
Soil is one of three filters. Hardiness decides whether a plant survives your winter, exposure decides whether it flowers, and only then does soil matter. A plant list that ignores any of the three is decoration.